1. Field of the Invention
The present invention relates to a folding door for opening/closing the entrance of all sorts of structure. More particularly, the invention relates to a half spread folding door wherein the door has a form of zigzag when it is fully opened, and the door has relative light weight and excellent rigidity so that it can be utilized at the entrance of large structure such as large depot and an airshed, etc.
2. Description of the Prior Art
Generally, since a large structure such as a depot of a grand scale logistic system, a warehouse of various industrial supplies, or an airshed must keep large articles, its entrance should be very large and its door has an extra large size which varies from several meters to a dozen meters in its width and height. Therefore, the door should have from several hundred kg to several ton in its weight, and its smooth opening/closing is a necessity and its high rigidity is required to resist an external force like a wind force.
Such a door can be employed as a sliding door for being thrust in a right/left direction, a folding door for being folded when opened and for being spread when closed, a swing door for being opened/closed centering around a shaft installed at one end of the door, and a shutter for being rolled up when opened and for being unfolded when closed.
However, it is very difficult for a swing door to adapt to an entrance of a large structure having very large size and heavy weight owing to its structural characteristic. Further, a sliding door, a folding door, and a shutter could be applied to an entrance of the large structure, but generally all of them must be operated by rotation force of a motor.
For instance, in Korean patent Laid-Open No. 2002-0028596, a sliding door for an airshed is described in which plural door members having suitable size are slidingly coupled to each other in an overlapping manner and are extended or shortened like a telescope. Further, in Korean Utility Model Registration No. 20-0227782, a sliding door is described in which plural door members are hingedly connected serially to move with a bending manner into a wall of an airshed or pull out from a wall of an airshed.
Furthermore, European Patent EP 1088959 A1 describes a folding door in which plural door leaves are hingedly connected serially to be folded or spread in a form of zigzag. More, Korean Utility Model Registration No. 20-0318037 describes a folding shutter in which plural slates are hingedly connected serially to be rolled up and unfolded in a form of zigzag.
However, in the conventional doors, each face of a door leaf is positioned on the same plane or the same direction and a rigidity of a door depends wholly on a materiality and thickness of the door. Thus, the door must be manufactured with a very deep thickness to secure the rigidity against an external force like a wind force and it leads to a problem in which a motor must require high consumption power to run a heavy weight door.
Further, as each door member is placed on the same plane when a conventional folding door is fully spread, relative high force is needed to fold the fully spread door and it is hard to make a folding operation smooth.
Particularly, in the case of a telescopic sliding door which is popular to an entrance of a large structure, the entrance has a big size and it calls for many door leaves. The horizontal cross-section of a door, which is necessary to operate a door, should be increased in proportion with a thickness of a door. It has a problem in that the door has occupied in a large space.